This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. The study involves determination of a rate of in vivo actin polymerization in steady-state conditions, based on FRAP measurements. This collaborative study collaborative studies involves development of cell-biological models that have potential for generalization and implementation in the Virtual Cell. Such studies, where models are necessary for data analysis and/or better qualitative understanding of cell phenomena, serve as motivators (and at the same time as testbeds) for further development of the Virtual Cell.